Apparatus for scanning



L A R E G R A B K C O T S C D PPARATUS FOR SCANNING original Filed Nov. 11, 1936 '7 Sheets-Sheet l @n kf Si my W39- D. c. sTocKBARGER ET AL 2,184,160

AARATUs FOR scANNING Original Filed N"ov. ll, 1936 7 Sheets-Sheet 2 19, 1939- D. c. sTocKBARc-x-:R er AL 2,184,160

APPARATUS FOR SCANNING Original Filed Nov. ll, 1936 '7 Sheets-Sheet 3 Dec. 19, 1939. D.. c. sTocKBARGER Er Al. 2,184,160

'APPARATUS FOR scANNING Original Filed`Nov. l1, 1936 7 Sheets-Sheet 4 FIGv " Dec'. 19, 1939.

D. C. STOCKBARGER ET AL APPARATUS FOR SCANNING j Original Filed Noir. 11, 1956 7 Sheets-Sheet 5 Flog.

D. C. STOCKBARGER LT AL APPARATUS FOR SCANNING original Filed Nov. 11, 195e vvsheets-sheet e D. 'wQKBARGER ET AL. 2,184,160

APPARATUS FOR SCANNING Original Filed Nov. 1l, 1936 '7 Sheets-Sheet 7 Patented Dec. 19, 1939 UNITED STATES `APPARATUS FOR SCANNING Donald C. Stockbarger, Belmont, and John L. Jones, North Billerica, Mass., assignors to Stockton Proille Gauge Corporation, Lowell, Mass., a corporation of Massachusetts Application November 11, 1936, Serial No. 110,258 Renewed October 30, 1939 28 Claims.

This invention relates to apparatus for scanning, and with regard to certain more specific features, to apparatus for scanning and thereby measuring areas.

Among the several objects of the invention may be noted the provision of apparatus for scanning wherein scanning beams are projected against a surface the area of which it is desired to measure in such manner that they sweep the median lines of contiguous increments, such as concentric circular increments, on the surface, and so conducting the scanning that the lengths of said median lines on the surface are photoelectrically integrated into an accurate expression of the area of the surface; the provision of apparatus of the class described which produces results characterized by their high accuracy; the provision of apparatus of the class described which is de,vv

signed, for example, to record scanned area increments on the surface to be measured at rates proportional to the linear speeds of the spots of interception of successive scanning beams on the surface to be measured; and the provision of apparatus of the class described which is relatively simple in construction and operation. Other objects will be in part obvious and in part pointed out hereinafter.

The invention accordingly comprises the elements and combinations o1' elements, and features of construction and operation, which will be exemplied in the apparatus hereinafter described,

and the scope ofthe application oi'which will be indicated in the following claims.

In the accompanying drawings, in which are illustrated several of the various possible embodiments oi' the invention,

Fig. l is a diagrammatic layout of apparatus embodying the present invention;

Fig. 2 is an enlarged diagrammatic vertical section of a typical scanning disc;

Fig 3 is a diagrammatic vertical section taken substantially along line 3-3 of Fig. 1, showing a workpiece, and the conical projection of a reilector on the plane of said workpiece;

Fig. 4 is a diagrammatic vertical section taken substantially along line 4-4 of Fig. 1;

Fig. 5 is an enlarged diagrammatic vertical section taken substantially along line 5--5 of Fig. 1;

Figures 6 and 7 are geometric iigures illustrating the design of rectilinear and polar coordinate cam elements, respectively;

Fig. 8 is a diagram of certain periodic timing devices and their electrical connections;

Fig. 9 is a longitudinal section, partly in elevation, of a one-turn clutch mechanism;

Figures 10, 1l, 12 and 13' are cross sections taken substantially along lines Ill-IU, |l-Il, |2-fl2 and l3-l3, respectively, of Fig. 9;

Fig. 14 is a diagrammatic layout of apparatus embodying an alternativeform of the present invention;

Fig. 15 is a diagrammatic section taken substantially along line 15-15 of Fig. 14;

Figures 16 and 17 are enlarged fragments of the device shown in Fig. 15;

i Fig. 18 is an enlarged vertical section taken substantially along line lt-l of Fig. 14;

Fig. 19 is an enlarged cross section taken substantially along line l9--l9 of Fig. 18; and,

Fig. 20 is a diagrammatic vertical section taken substantially along line 2li-2U of Fig. l.

"Similar reference characters indicate the corresponding parts throughout the several views of the drawings.

Referring now more particularly to Fig. 1, there is shown, in somewhat diagrammatic form, a lay.

out of apparatus which embodies the present invention. Numeral i indicates a scanning disc, which will be described more fully hereinafter. 'I'he scanning disc i is plane and is mounted for rotation on a shaft 3 in such a manner that the plane of the disc i is perpendicular to the axis of the shaft 3. The shaft 3 is driven by a differential 5, to be more fully described hereinafter, the opposite side of which differential 5 is driven by a main drive shaft l. rlhe shaft 3 is provided with thrust bearings 3 and il and with a substantially constant brake l2. The shaft l is driven by a motor i3 acting through a one-turn clutch it and a gear reduction box l5. The scanning disc i is provided with a spiral series of scanning holes il (see Fig. 20), the arrange-y ,l

ment of which will be described in greater detail Numeral l indicates a light source, such as an incandescent filament lamp. Numeral 2| indicates a lens, which is placed between the light source i9 and the disc I, and which focuses an image of the light source I9 on a second lens 23, placed on the other side of the disc l. The axis of the lens 2| coincides with the axis of the lens 23 which axis is parallel to the axis of the shaft 3 of the disc l. A light shield 24 is desirably provided in such position as to enclose the light source I8 and lens 2 I, and prevent stray light from entering other parts of the apparatus. The image of the light source I9 should fill the second lens 23. The second lens 23 is arranged hereinafter.

to focus an image of a hole I1 in the scanning disc I on a work piece 25, the area of which it is desired to measure. mounted at a predetermined distance from the 5 lens 23 and with the plane of the work piece parallel to the plane of the disc I. Lenses 2i and 23 are not ordinarily single elements as shown diagrammatically in Fig. 1, but are preferably highly corrected compound lenses, such as 10 microscope and camera lenses, for example. Behind the work p'iece 25, but as close to it as practically feasible, is placed a reflector 21, which, in the present embodiment, is a substantially spherical mirror. The reflector 21 is disposed to rem ilect light beams issuing from the lens 23 and not intercepted by the work piece 25, to a photosensitive device 25, which is desirably placed as close to the lens 23 as possible.

, Y Between the lens 23 and the disc I is an opaque go diaphragm or mask 23 (Fig. 20) of steel, for exfield 0f the lens 23, and is likewise Such tht its conical projection (using the optical center of lens 23 as an apex) on the plane of the work 3g piece 25 (see Fig. 3, wherein this projected image of the aperture is shown and indicated by numeral 32) is large enough to include any work piece it is desired to measure with the particular set-up of apparatus. The size and position of the reflector 21 are such that its conical projection on the plane of the work piece 25 overlaps or extends beyond the said conical projection ofthe aperture 3l on the plane of the work piece 25.

The photosensitive device 2! is connected electrically to an amplifier 3i, constructed to suit the characteristics of the particular device 29 employed, and the amplifier is in turn connected to a relay 33. 'I'he relay 33 is interposed in a circuit connecting power wires 34 to an electromagnetic clutch 35 through a second relay 36. Relay 38. is controlled by periodic timing devices 31 and 38 (hereinafter to be described) which are driven directly by the shaft 3. One end of the clutch 35 is driven by a shaft 40 through gears 39 in turn driven by shaft 1. Gears 39 are in a one to one ratio, so that shafts 1 and Il rotate at the same speed. The other end of the electromagneticA clutch 35 drives a shaft 4I, which drives a multiplier gear 32, which drives 54. A releasable coupling 45 is provided between the electromagnetic clutch 35 and the shaft 4I for releasing the shaft 4| from the electromagnetic clutch 35 so that the counter M can be reset by means of a hand wheel l5 after the conclusion of a measurement of area. The multiplier gear 42 cooperates with the counter 44 to permit the measurement to take place in the desired units of area. A substantially constant brake 41 is provided on the shaft 43.

The multiplier gear l2 and the counter Il, taken as a unit, are carefully calibrated so that the rotation of the shaft lIA through a given angle from a well dened starting position produces a known change in reading of the counter u, and the shaft 4I is provided with a coupling 45 and a hand wheel 43 for returning the shaft 4I to the starting position after the conclusion 'of an area measurement, said starting position 'I'he work piece 25 is` a shaft I3, which drives a rotation counter device arcaico being such that the counter reads zero, for example, all backlash between shafts 6I and 33 having been removed by turning the hand wheel 46 in thel forward direction. A braise I1 on shaft 33 cooperates in eliminating error due to 5 backlash.

The electromagnetic clutch 35, as well as the counter M, are of the customary construction nnding use in this and allied arts. Suitable devices of this character are shown and de- 10 scribed in greater detail, for example, in our copending application Serial No. 90,260, flied July 11, 1936.

'I'he principles of operation of the apparatus thus described are presented in the following u paragraph, assuming for the moment that the differential 5 drives the shaft 3 at the same rotational speed as the speed of the shaft 1, and that the shaft 1v rotates at constant speed. As will be pointed out hereinafter, the rst condition is not ordinarily encountered in the operation of the apparatus, not is it necessary for l the speed of the shaft 1 to be constant. Howl ever, these assumptions are of aid in describing th general principles of operation of the appau ra us.

The holes I1 in the scanning disc I, passing between the lenses 2| and 23, project beams oi' light towards the reector 21, each hole I1 producing one beam winch sweeps the reflector as the disc rotates, and the successive holes I1 producing successive beams which sweep the conn bination of reflector 21 and work piece'25 at different angular positions.- As long as these beams are not intercepted by the work piece 25, they are reflected back by the reilector to the photosensitive device 23, causing a response therein. 'nie response of the photosensitive device is amplified by the amplier 3l, and the amplifier current holds the relay 33 (in the prent embodiment) in open-circuit position, so that no power passes to the electromagnetic clutch 35. This means that no driving connection is hadbetweenthe shafts 1 and 4I, and hence the counter 44 does not operate. The instant, however, the beam of light (which will hereinafter be referred to as the scanning beam) B intercepted by the work piece 25, the actuating light on the 4photosensitive device 25 stops. thus causing the amplifier current to drop below the value required for holding the relay 33 in open-circuit position. The relay 33 thus closes, passmg power to the electromagnetic clutch 35, which thereupon operates to drive-the shaft 4I from the shaft 1. The counter 33 then commences to operate. The operation of the relay 35 is here disregarded, it being assumed that it does not interfere with the action of the relay 33 in passing power to the clutch 35.

The rotation of the counter Il, it will be seen, is proportional to the rotation oi' the scanner disc I during the time that the electromagneticclutch 35 is operating, under the assumption as to the action of the differential 5 stated above. If, therefore, the rotation oI.' the disc I can be made proportional to the length of the line on the work piece 25 traced by the moving scanning beam, then the value on the counter will be true measure of the length of said line, and If 70 it be assumed that the said line is the median line of anincrement of constant width on the work piece, then the counter reading becomes an'expression of the area of said increment.

Foranyonescanningbeamitwillreadily' seen that the above conditions are fulillled. because the linear speed of a spot of light rcpresented by the interception of the scanning beam on the work piece, as the beam sweeps across the piece, will be directly proportional to the angular speed of the disc I. But a diilculty arises when successive scanning beams are considered. A beam from a scanning hole of lesser distance from the center of the scanning disc will move along the surface with the same angular speed as a beam from a scanning hole of greater distance (with the assumed constant angular speed of the disc I), but due to its said lessed distance, the linear speed of the spot produced by the beam from the less distant hole on the Work piece will be less than the linear speed of the spot produced by the beam from the greater distant hole. And, it will be seen, the linear speed of the spot is the true measuring factor of the area (or length of scanned line) on the work piece.

In the scanning disc I of the present embodiment, the holes I1 are arranged in a spiral mannersuch that the radial distance between adjacent holes is equal. InA other words, referring to Fig. 2, which shows, for illustrative purposes, a greatly simplified scanning disc I having but seven holes I1, the difference between the distance (Rs) of an outermost hole I1. from the center of the disc I, and the distance (Re) ci the next inward hole I1 on the spiral from the center of the disc I, is the same as the diil'erence between the distance Rs of the said hole Il and the distance Re of a next inner hole on the spiral I1c. I'his same diierence is likewise found between the distances (Rb, Re, Rd, Re, Rx, and Rg) of successively inward holes I1e, lla, IIe, Illr, and I1, on the spiral.

The equal radial spacing of the holes I1 on the scanning disc i provides for the scanning oi increments of equal widths on the work piece @hier each of the said holes I1. This statement will be better understood by reference to .1W 3.

In Fig. 3 the light broken lines indicate the conical projections of the paths scanned by the beams produced by the several holes I1 in the scanning disc I, said conical projections being on the plane of the work piece 2i and the center ci the cone of projection being at the optical center of the lens 23. Fig. 3 indicates the paths scanned on the work piece 2i and on an imaginary plane reflector placed in the plane of the work piece 25. 'I'he line designated as Re represents the conical projection of the'scanned path ci the beam produced by the hole I1. in the disc I, and the broken lines designated as Rs. Re, Re, Re. Rf, and Rg are, respectively, the conical projections of the paths of the scanning beams produced by holes I1s, Hc, |14, |19, I1r, and Ilm. The increment represented by the line Rs extends from the solid Ylight line Ri to the solid light line Rn, and the diiIerence in radii oi the lines Ri and R2 (designated as h"), is equal to the constant differences between the radii oi' broken lines R., Rb, Re, etc. The value h accordingly represents the width of the incremental path scanned by any one of the holes I1.

Since all of the scanned increments of a work piece iid are thus of equal width, equal areas will be measured by equal lengths laid out on the broken lines Rs, Rb, Re, etc. If, therefore, all of the sc beams from all of the holes I1 can be made to move across their respective paths Ra, Re, Re, etc., on the work piece 25, at the same linear speed, then each scanning beam will measure area at the same rate (so many square units per unit of time) as all of the other scanning beams. Under such conditions, the operati'on of the counter 44 becomes a time function, the counter being arranged to operate only during such intervals of time as the scanning beams are intercepted by the work piece 25.

A problem, however, arises in securing equal linear speed for all of the scanning beams from all of the holes I1 across the work piece 25. This is because the said scanning beams are produced from the stationary light source I9 by holes I1 which travel in concentric circular paths, the paths of course being of various radii. If the scanning disc I is driven at a constant angular speed, it will be seen that the desired condition, A

namely, equal linear speed of all scanning beams on the work piece 25, 4cannot be secured.

The differential 5 provides the means, in the present embodiment of the invention, for correcting the speed of rotation of the scanning disc I so that the desired condition is achieved.

The parts of the diilerential 5 may be described as follows: Numeral 48 indicates a bevel gear which is non-rotatably secured on shaft 7. Numeral 49 indicates a bevel gear of identical size and pitch, which is non-rotatably secured on the shaft 3. An extended portion 5I of shaft 1 rotatably supports a differential case with a peripheral spur gear 53, which is of greater diameter than the gears 41 and 42. A bearing 55 permits the case 52 to turn freely on the extended portion 5I of shaft 1. suitably mounted in recesses 51 in the spur gear I3 are a pair of tumbler gears 59. The tumbler gears l! are of Identical size, and are bevelled at a proper angle to mesh with the gears 41 and 48, to provide a driving connection therebetween.

It will readily be seen that, provided the spur ear 53 is held stationary, them gear 41 drives the gear 49 through the tumblerl'.i"gears 58 at a one to one ratio, whereby the shafts 1 and l rotate at the same angular speed. However, ii' the spur gear 53 is rotated, then by the laws of differential action, the shaft 3 is advanced or retarded relative to the rotation of the shaft 1 by an amount determined by the extent and direction of rotation of the spur gear 53.

.In the present embodiment of the invention. rotation of the spur gear 53 is achieved in the desired manner by means of a' vertically slidable rack 6I, the face of which rack 6I meshes with the teeth of spur gear 5l, and the lower end of which rack 6I carries a wedge-shaped cam follower 63. 'Ihe follower 63 engages the edge ot a cam 6I, which is mounted on a shaft i1, and the follower I3 is at all times held positively in contact with the cam B5 lbya spring ll. 'I'he cam 66 is statically balanced about the axis of the shaft 81 by means of a counterbalance Il. The shaft 61 is driven to rotate in a one to one ratio with the rotation of main drive shaft 1, by means of gears 10, 1I, and 12.

The design of the cam 05 to achieve the desired result through the dliferential i will next be described. Fig. 7 shows the progressive stages of design.

It is assumed, for purposes of illustration, that the desired scanning disc is to contain seven holes in the spiral, as shown in Fig. 2. It is also assumed that each of the holes is separated from its adjacent hole by an angular` distance a. This 76 angle 1 is also the angle subtended by the sides of the sector-shaped opening 30 in mask 28. In order to provide a dead region for permitting the return of the cam follower to its innermost. position and for other reasons hereinafter set forth, a dead angle is provided. Because of the relatively small number (seven) of holes which was assumed for sake of clarity in illustrating the method of cam design, the angle a is relatively large in Fig. 2, necessitating a relatively large mask aperture 30, which in turn would necessitate a relatively large lens system 2| and 23. However, in commercial practice the number of holes in the scanning disc will ordinarily be largely in excess of seven (say, for example, iifty or so) as shown in Fig. 20, and the angle a will consequently be relatively small, making it possible t0 use lenses of more reasonable diameters, as indicated in Figures l and 20.

The cam is designed to impart a linear motion to its follower 63, of a: units of displacement per a radians of angular motion of the cam 65. Since the angular speed of the cam 65 is constant, relative to the angular speed of the main drive shaft 1, and since displacement oi' the cam follower 63 acts through the differential to produce angular motion of the scanning disc I relative to the cam, the disc I is given the required change in speed to compensate for the change in radii of the several holes I'I. The cam follower 63 returns to its innermost position on the cam 65 during an interval following the sweep of the scanning beam from hole IIg. During this same interval, the scanning disc I loses its advanced angular displacement.

To simplify the calculations of the shape of the cam 85, it is assumed that the scanning disc I will have seven holes II, with the outermost hole |15 at a radius cf 6.95 inches, and with each hole on the spiral 0.10 inch closer to the center of the disc I. This means that the innermost hole Il, on the `spiral will be 0.60 inch closer to the center of the disc I than the outermost hole I'In.

Linear motion of the rack 6I produces angular displacement of the scanning disc I, relative to the main drive shaft l, in direct proportion. Therefore a linear rack speed of z units per second produces an angular speed of ka: radians per second. 'Ihe factor k is determined by the size of the linear displacement unit, the dimensions of the cam 65, and the diameter of the differential spur gear 53. The factor k can also be given 'any desired value by introducing a gear train between the rack 6I and spur gear 53. Therefore it is sufficient to design the cam 65 to impart units of linear motion during a standard time of sweep (defined hereinafter), :c being in each case proportional to the deficiency in area measuring speed relative to the area measuring speed of the outermost hole Ila on the spiral. The standard time of sweep is defined herein as the time which would be required for the disc I to rotate through a given angle a, indicated in Fig. 2, for example, if no cam 65 were used. Actually, as will be seen hereinafter, the cam 65 acts to reduce the time of sweep of successive holes I1. Therefore the displacement of the cam follower 63 must be correspondingly less than :r to make the added speed proportional to m.

In the following Table I, certain factors are set down relative to the assumed scanning system. The first column of the table merely identifies the particular hole I1 in consideration'. The second column sets forth the distance (Rm) oi' that hole from the center of the disc. The third column sets forth progressively the radii (Re) of -the increments scanned by the beams produced from the particular holes, corresponding to the values R1, R2, etc., in Fig. 3. For purposes of the present calculation, it i`s assumed that the radii of the increments on the work piece 25 are the same as the radii of images of these increments projected on the disc I by the lens 23, since, in any event, these values in any properly designed system would be proportional to each other. The fourth column sets forth the difference (ARm) in distances of the succeeding holes I 1 from the center of the disc I. By the initial assumption, this expression ARm is constant for all holes, with the values of 0.10. 'I'he fifth column sets forth the progressive summation (EARm) of the values ARm from hole to hole. The sixth column sets forth the relative area (A) included in a circle of a radius R., which is proportional, and hence taken as equal to, the square of such radius. The seventh column sets forth the difference (AA) in area for the successively shorter radii, and may be conceived of as an expression of the actual area. of the increment scanned by the particular hole. 'I'his value, AA, can also be conceived of as the area scanned per unit of time, assuming constant and unchanging disc speed, f or each of the holes Il. The eighth column sets forth the differences between successive values of AA, expressed as MAA). This eighth column shows values, it will be seen, that are all one-fifth of the corresponding values of ARm, as set forth in the fourth column. The ninth column sets forth the progressive summation (2A(AA)) of the values of MAA).

Table I Radi imi" us ive n- EA Hole R R. AR.. MR.. eluded AA MAA) (AA) ureaA 40.00 000 17..... 0.05 1.39 47.01 0.02 0.02 175.-.. 0.85 1.37 40.24 0.02 0.04 17..... 0.75 1.35 44.89 0.02 0.05 17...-. 0.05 1.33 43.50 0.02 0.00 17..... 0.55 1.31 42. z5 o. 02 0. 1o 17f.... 0.45 1.29 40.90 0.02 0.12 17,.... 0.35 1.27 39.09

From the foregoing table. it will be seen that either the value EMAA) or the value EARm can be taken as x, z having been heretofore dened as proportional to the deficiency in area measuring speed. Y

As hereinbefore stated it is purpose of the cam-controlled differential 5 to correct the speed of rotation of the scanning disc i by advancing it relative to the rotation of the shaft l. Since tlm holes il are equi-radially spaced and therefore the widths h of the scanned strips on the work piece 25 are equal, the area scanned by a given beam per unit of time measured in terms of the angular displacement of the shaft 'l is where A is the angular displacement of the disc I, Rm is the mean radius of the circular path of the hole l1 about the axis of the shaft ts is the angular displacement of the shaft I and C ChAR..

to be constant, either A or ts (or both) must have predetermined different values for each chosen constant and therefore ts has a series of Values such that is constant. Regardless of the choice, however. the cam 65 lags the disc I in its rotation. Therefore an angular correction must be applied to the lay-out of the cam 65 or of the disc (or both) depending on the choice of the speed correction guiar correction is applied to the lay-outer the cam in two ways as will be described hereinafter.

Table II (set forth hereinafter) shows the application of this correction. In Table II, the rst column again gives, for identification, the designation of the particular holes on the disc The second column sets forth the speed correction determined from Table I, and expressed as the vaines given in Table I for the quantity EARm. -In Table II, these values arefdesignated as (a). Column three sets forth the angular correction (b) suggested in the preceding paragraph. This angular correction (b) is the ratio oi' the area scanned by a given hole I1 to the area scanned by the outermost hole |11 during unit angular displacement of the disc in each case. (b) is therefore the desired angular displacement t5 of the shaft 1 during displacement oi the disc i through the angle a, te being expressed in arbitrary units such that it is unity v for the outermost hole Ila in the disc That t.; should be correspondingly less than unity for y other hole I1 than the outermost hole |18 is evident since a givenv angular displacement of the disc l results in the scanning of a smaller area than would be scanned bythe outermost hole ils and therefore the shaft 1 must rotate through a correspondingly smaller angle in order u that the counter 4I cannot register a number which is too large. Since A is chosen constant it is evident that the desired linear displacement oi the cam follower B3 is the product of the speed correction (a) and the angular correction (b), because (a) is the linear displacement of the cam follower 63 per unit rotation of shaft 1 and (b) is the magnitude of the rotation ts.

.The fourth column of Table II sets forth the corrected speed correction (ab), which is the product of the speed correction (a) and the angular correction (b) The fth column sets forth the progressive summation (2(abl) of the values set forth in the fourth column. The sixth column 70 sets forth the values for the expression (l-b).

The seventh column indicates the progressive i i n u tion (2XL-bl) of the values set forth in the sixth column. The last value in the seventh column, 0.3022, represents, when multiplied by n the angle a, the number of radians that the disc value of Rm. In the present embodiment, A is method. l.In 'the present embodiment the anthe cam G5, using'rectangular coordinates.

will be advanced in excess at the end of the scanning.

Table II Speed Angular Hole correl (ab) Mob) (1-6) E 1b Vreference line 11a (shown as a short dashed line) isl drawn. Successive angular intervals of a radians are next laid out, and defined by short dashed lines 11b, 11e, 11d, 11e, 11x, 11g, and 11h.

The angular distance between the lines 11h and 11a represents the dead space angle on the cam.

A circle 19 is now described around the center 15, atta radius equivalent to the desired innermost edge of the com.

The next procedure is to lay out lines 8| representative of the angular corrections necessary. These lines 8| are all shown aslong dashed lines in Fig. '7. 'I'he positioning of the lines 8| is de- Y termined by the values for 2(1-b), as expressed in the seventh column of Table II, The first such line 8 Ic is laid out at an angular distance equal to 0.01440 radians behind the line 11e. The second line Bld is laid out at an angle equal to 0.04320; radians behind the line 11d. Successive lines Ble, 8h, 8|g, and 8|h, are similarly laid out with respect to the lines 11e, 11:, 11g, and 11h. The lines 8| and BIB are located, respectively, on top of the lines 11b and 11a, for the reason that the line 8|. is a reference line, and positioned identically to the reference line 11a, while the correction factor (EG-w) for the line 8|, as shown in the seventh column of Table II', for the first hole, is zero.

A scale is now chosen for the values of the expression 2mb), as given in the fifth column of Table II. 'I'his scale is established by the diam-A eter of the spur gear 53, and certain other factors, as heretofore expressed in connection with the denition of the constant k. The scale used in Fig. 7 is entirely arbitrary. 'I'he values from the fifth column of Table II are now laid out progressively on the lines Ble, Bld, 8|e, etc. The zero point is considered as the circumference of the circle 19. Hence. the edge of the cam itself, on the lines 8| s and 8| will be the edge of the circle 19, since the values of the expression 2mb) for the reference line 8|. and the second line 8|s are both zero. The point online 8| is at a distance of 0.0986 unit from the circumference of circle 19. Similarly, the point on line Bld is at a. distance of 0.2928 unit from the circumference of circle 19, and the points on the succeeding lines 8|e, 8h, Slg and Bln are similarly established.

`The correct method of connecting the points thus established is illustrated in Fig. 6 in which the linear displacement of the cam follower 63 is plotted against the angular displacement of lines 82g, 82h. 82e, 82a, 82e, 82:, 82g, and 82h, the object being to produce constant linear speed of the cam follower 63 relative to the speed of rotation of the cam 65 during the time of each sweep. The desired constant linear speed of the beam across the surface of the work piece 25 is obtained by adding a constant speed to the speed of the shaft 1, both of said constant speeds being of.

course relative to the speed of the shaft 1. Fig. 6 could be used to construct a linear cam which could be used to supply the desired speed corrections to the disc I if said cam were given a constant linear speed relative to the speed of rotation of the shaft 1. The line, obtained by connecting the points in Fig. 6 by straight lines, when transferred to polar coordinates is shown in Fig. 7 by line 83. While line 83 appears in Fig. 7 to be a smooth curve from line 8Ib to 8Ih, it will be seen from the manner in which it has been constructed from Fig. 6, it is in reality a series of sectors of Archimedean spirals of varying pitches. Section 83g. of line 83 (line 8h; to line 8Ib)., being taken from line 82s, has zero pitch. Section 83h (line 6h to line 8Ic) has apitch determined by'the slope of line 82h. Likewise, sections 83e, 83d, 83e, 63f, 83g, and 83h have pitches determined by lines 82C, 82d,'82e, 82f, 82g, and 82h. The intersections of the several sections of line 83 are so gradual on the scale chosen for Fig. 7, that they do not show the cusps that are really present, vbut appear as a continuous, smooth curve. The return por tion of the cam, represented by the straight line 85. may be located exactly upon the line 8in.

By following the principlesset forth above in connection with the design of a cam for a disc of the assumed characteristics, a similar cam may be designed for discs with any other assumed characteristics, such as a greater number of holes.

In the design of the cam 65 hereinbefore described, it has been assumed for sake oi. simplicity that the follower 63 has a sharp wedgeshaped bearing surface, the angle of the wedge apex being sufliciently small to insure contact between said apex alone of the follower 63 and the cam 65 at all times when accuracy of follower displacement is desired, that is throughout the actual scanning process, said assumption serving to eliminate follower corrections from' the calculations of the dimensions and shape of the cam` 65. If desired, the design of cam 65 can be modified to permit the use of another type of rfollower 63 such asa roller, for example, retaining the desired relation between the displacement of the follower 63 and the rotation of the cam 65. For a. roller follower, it is necessary to introduce both radial and angular corrections into the design of the cam 65, because the point of tangency of such a roller follower to the cam is not always on the line connecting the cam center to the roller center.

The cam 65 should be set at such an angle on its shaft 61 that follower 63 enters section 83B of cam 65 (e. g., crosses line BIB) at the same instant that hole |15 of the disc I passes into the eld of the aperture 39 of. mask 28. If this is so, then each subsequent hole I1 will pass into the field of aperture 30 just as the follower 63 reaches the proper section 83 of the cam 65.

The effect of the cam 65 as thus designed, when employed together with the differential 5 and the disc I suited to the cam, is to cause the disc I to rotate at a series of constant angular speeds, such that the scanning beams produced by all the holes i 1, at their point of intersection on the work piece 25, move with substantially the same linear speed. In other words, all of the scanning beams move at such speeds that they measure a predetermined substantially constant number of area units per unit of time. Substantially the same number of units of area are measured by a scane ning beam from the innermost hole I1g, in unit time, as are measured by the outermost hole Ila, 5

Therefore, by 10 be recalled, was one of the principal objects of the 15 present invention.

It is now evident, however, that the assumption of constant driving speed of shaft 1, which was introduced hereinbefore for purpose of simplicity, is unnecessary, because all moving parts of 20A the scanning apparatus move with predetermined relative speeds and therefore the counter 44 increases its reading by a uniform amount for successive units of area scanned.

In the system described the relay 33 is so de- '25 l signed that when no light beam reaches the photo-sensitive device 29 the electromagnetic clutch 35 is energized and therefore shaft 1 is mechanically connected to shaft 4I so that if/ shaft 1 turns while no light beam reaches the `30 photosensitive device 29 the counter 44 increases its reading. Not only during the times that light beams are intercepted by the work piece 25 does the photosensitive device 29 receive less light than is required to operate the relay 33 through 35 the amplifier 3i, but also during at least a part of the time that the cam is rotating through the angle p plus 030220:, for example, no light beam reaches the photosensitivedevice 29. During the return of the cam -follower 63 to its innermost .40 position on the -cam 65 the disc I loses its ad,.

vanced angular displacement relative to the cam 65 and therefore the last hole I1 in the-disc I moves back across the aperture 30 in the mask 28 through a fraction of the angle a and subse- 45 quently re-scans through the same angle and does said re-scanning at reduced speed. It is readily understood therefore that unless the external electrical circuit of the relay 33 and the electromagnetic clutch 35 is closed and opened50 precisely at the beginning and end, respectively, of the scanning process an error in area measurement may result` To close and open the external circuit of the relay 33 and the electromagnetic clutch 35- at the required instants, the two accur 55 ate periodic timing devices 31 and 38 hereinbeiore referred to are provided, and are driven by shaft 3 to control relay 36, which relay 36-con trols said external circuit.

Periodic timing devices are sufciently well U0 known to those skilled in the art that no detailed description is necessary herein. Said devices (see Figures l and 8) comprise relatively slowly-rotating pairs of slip rings and 31, respectively, con

nected in series with relatively fast-rotating pairs Am5 of slip rings 89 and 9i, respectively. The rings 89 and 9| are driven by shaft 3 through a gear train 93. Periodic timing devices of this character are often used in clocks, for example, to

close (or open) electrical circuits precisely at pre- 70 determined times once each hour, for example. In the first embodiment of the invention herein described the periodic timing device 31 is used to close the electrical circuit of the on solenoid 91 of relay 36 once each time the shaft 15 lil said external electrical circuit. loi power it is provided for both relays it and 36. A The function ci the one-turn clutch mechaarcaico t has rotated through 360 degrees with an angular deviation from 360 degrees of 1 part in 2401, ier example, and said device 3l is `adjusted to close said circuit at the beginning of the scanning process, which is the time when the first light beam is permitted bythe mask it to begin to sweep across the combination of reflector il and worn piece it.y Periodic timing device it is identical with periodic timing device 3l but is used to close the electrical circuit t@ of the off solenoid iti of the relay t at the end of the scang process, which is the time when the last light be has just completed its sweep across the combination ot reector 2l and work piece 25.

Relay to, as shown diagrammatically in Fig. 8, is a self-holding relay ci the type. commonly used with a push-button control to stop and start motors. Said relay it is so connected electrically to the periodic timing devices tl and it that periodic timing device 3i closes the external electrical circuit of relay 03 and electromagnetic clutch it whereas periodic timing device it opens A suitable source nism it to be described in greater detail hereinafter, is to aid in preventing the measurement of a given work piece 25 more than once. In the system as shown in Fig. l the drive shaft |05 of the one-turn clutch it is continuously rotating, but driven shaft 7| rotates only one complete revolution and only after a manual operation has been performed. The one-turn clutch l0 is adjusted to start and stop the rotation of the shaft 'l when the cam follower t3 is in contact with the cam it at a point within the dead angle s, said point being near the intersection ci line iii. with the circle it.

rThe construction of the one-turn clutch mechanism iii is as follows:

The one-turn ciutch mechanism, It is shown in greater detali in Figures 0, 10, l1, 12, and 13, to which reference is nowdirected. The main drive shaft itt is keyed to a rotating outer-sleeve member |ti. An inner cam member |00 is mounted for rotation within the sleeve member itl, and has peripheral recesses for receiving rollers itil. The cam member itt has a cylindrical portion Mt, on which rotates a second sleeve ill. 'll'he sleeve iii has a cylindrical retainer ring portion iii which extends into the sleeve member iti'l and retains the rollers iii. vlihe sleeve iii a peripheral projection or stop iii.

The cani member itt is outwardly hanged beyoud the end oi the sleeve ill, providing a groove titi therebetween, and a cylindrical part beyond the groove titi. The cylindrical part titi l has a peripheral projection or stop |27. Beyond .iii

the cylindrical part itt is another cylindrical part tit ci lesser diameter, said cylindrical part tit iorming the drum oi a brake im. This brake ii| can be used with relatively light pressure to aid in stopping the rotation oi the cam member iti, but is adjusted in any case so that it does not prevent the stop itl from making contact with an end itt oi the latch itt, hereinaiter to be descri d pair ot pins itl and it@ are mounted, oppcsitely facing, on the cam member and the sleeve its respectively, and a tension spring iti, lying in the groove |23, connects the two pins.

The drive :il l is received in, and keyed to rotate with the cam member lili.

literal itt indicates the hereinbeiore-mentioned sliding latch that is supported for sliding movement in bearings |03 and ist. The latch |35 is provided with a handle It'l at its free end, and a tension spring M9 reacts between a collar itl made fast to the latch |35, and the bearing M3 to cause the latch |35 to be normally in a retracted position suchthat the opposite end |33 of the latch |35 is positioned under the projection |2| on the sleeve lil, in such manner as to prevent the rotation of said sleeve ill and is positioned under the projection lil on the cam member |09 in such a manner as to prevent the rotation of the cam member |09.

Normally the sleeve |07 rotates continuously with the shaft |05, but the sleeve and the cam member |09 cannot rotate with the sleeve |01 because the stops 2| and |21, respectively, are held back by the end |33 of latch |30 This holds the roller retainer H9 in such position that the rollers ||3 are idling, being incapable of establishing a driving connection between the sleeve |01 and the cam member |09 and the angle subtended by the stops |2| and |21 at the axis of the shaft 7| is zero. However, the instant the latch |35 is manually moved out of locking position, by pulling the knob lil, the spring lili, reacting against the inertia of the moving parts of the scanning apparatus and'against the friction of the various bearings in the scanning apparatus such as the bearing of shaft l, for example, rotates the sleeve enough forwardso that the retainer Ht brings the rollers H3 into a driving connection between-the sleeve |0l and the cam member |09 the angle of rotation of the sleeve being which angle is small relative to' the dead angle on the cam tt. The cam member |09 thereupon commences to rotate, carrying the sleeve lil and shaft p7 with it and the angle subtended by the stops |2| and |21 is the displacement angle Meanwhile, the knob lil has been released, permitting the latch |35 to return to a locking position, so that, immediately upon the completion of a single revoluton, the sleeve l il is stopped by the re-engagement of the stop |2| with the end |33 of latch |35. ,l

The stopping of the sleeve moves the retainer its so that the rollers H3 are again brought to idling position. The rotation of the cam member |09 ceases when the stop |27 on cam member |09 engages the end |33 of latch |35. The D,

excess rotation of the cam member it@ relative to the rotation of the sleeve stores tension in the spring Mi for the next revolution. Snce the mechanical conditions are substantially identical for successive operations, the revolution of the cam member |09, and hence of the shaft l, is substantially one turn for each manual operation of the knob Itl.

It is evident, however, that should the oneturn clutch It become worn after long use and consequently occasionally turn through an angle greater or less than 360 degrees, no error in the area measurement can result, because the maximum angle through which sleeve can rotate, relative to the shaft l, is a small angle relative to the dead angle ofthe cam 65, and the one-turn clutch it is adjusted to start and stop the shaft l', when the cam follower 63 is in contact with the cam 65st a point within the dead angle s, said point being. near the intersection of the line tls with the circle 19. The one-turn rclutch it cannot rotate through an angle less than 360 degrees minus because said clutch i0 must continue torotate with the shaft |05, after lrelease of the stops |2| and itl through temdit -from their contact with the cam member |01.

The same features of design, which prevent the rotation of the one-turn clutch |4 through an angle less than 360 degrees minus 6, also prevent the rotation of the one-turn clutch through an angle greater than 3.60 degrees plus Rotation'of the one-turn clutch |4 through an angle greater than 360 degrees can result only from initial displacement of the sleeve ||1 relative to.

the cam member |09 through an angle less than 6, before the release of the stops |2| and |21 through the temporary manual withdrawal of the end |33 of the latch |35, -and from ilnal displacement of the sleeve ||1 relative to the cam member |09 through an angle lless than said initial angle.

Rotation Aoi the one-turnclutch I4 through an-angle greater than 360 degrees can -result in no error in area measurement because said rotation is positively stopped when the y cam 55 reaches such an angular position that the cam follower 63 is in contact with the cam 6 5 at a point Within the dead angle of the cam 65.

Angular deviations of the rotation of the oneturn clutch |4 from one complete turn cannot accumulate to exceed an angle greater than ,4

in either direction, during any number of scanning cycles because the angular position of the latch |35 about the axis of the shaft 1 is fixed, and contact of the stop |2| with the end |33 of the latch |35 is a necessary condition for both starting and stopping the rotation of the one-turn clutch |4.

Thus it is clearly shown that the operation of the one-turn clutch I4 cannot produce an error in the measurement of area because the starting and stopping of the rotation of the shaft 1 always occur at instants when the cam 65 is in such an angular position that the follower 63 is in contact with the cam 65 ata point within the dead angle of the cam 65 and no hole |1 is in position, relative to the mask 23, to scan,

and the external electrical circuit of the relay The motor I3 is started, thus commencing the rotation of the shaft |05. The lamp |9 is turned on, so that the production of scanning beams can be commenced. The-latch- |35 is in its locking position, so that the shaft 1, and all moving parts driven by shaft 1 are stationary. The electromagnetic clutch 35 is electrically disconnected from the relay 33 by relay 36. The work piece, 25, the area of which it is desired to measure, is now placed in position in front of the reflector 21. Thereupon, the knob ,|41 is pulled, and the one-turn clutch I4 permits the shaft 1 to begin making one revolution. At the beginning of the scanning the relay 36 electrically connects the electromagnetic clutch 35 to the relay 33. During the one revolution of the shaft 1, a complete series of scanning beams,

produced during the one revolution of the scanning disc is produced, and each scanning beam actuates the photosensitive device 29 in accordy ance with its interception or non-interception by the work piece 25. During this interval, the electromagnetic clutch 35 is under direct control of the relay 33, which is in turn under direct control of the photosensitive device 29. In the I system as described, this control means that whenever the scanning beam is intercepted by the work piece 25, the electromagnetic clutch 35 is energized so that the shaft 40, as driven by shaft 1 through gears 39, drives the shaft 4|, and hence drives the counter 44, thus accumulating a measurement of the area of the work the electromagnetic clutch 35 from the relay 33.

At the completion of the one revolution of the one-turn c'utch |4 the shaft 1 stops rotating.

It is thus seen that, through the operation of the one-turn clutch I4, the number of scanning beams for any one work piece 25 that are edectual to operate the counter 44 is limited to one complete set of scanning beams, and' no repeat of measurement of one or more increments of the work piece 25 can take place. It is also thus seen that, through the operation of the periodic timing devices 31 and 38 the counter 44 is automatically prevented `from increasing its reading when no scanning is taking place even if the shaft 1 is rotating. s

In the embodiment of the invention vshown in Fig. 1, the description of which has just been completed, a factor of importance is that the differential 5 has been introduced-into the drive.

of the scanning disc and operated in suchl manner that the rotation of the counter 44 is proportional to the linear speed of the scanning beams as they sweep across the work piece 25.

In the Fig, 1 embodiment, this result has beenl achieved by driving the shaft 43 of the counter 44 at a speed proportional to the speed of the motor |3 and then so driving the scanning disc |v that all of the scanning beams move across the work piece 25 with the same linear speed relative to the rotational speeduof the counter 43. It will readily be seen that the same result can be achieved if the differential 5 is introduced into the drive of the counter 44, say, for example, between the gear 39 and the electromagnetic clutch 35. scanning disc can be driven directly from the main shaft 1. With such an embodiment, it will be seen that the'angular speed of the drive for the counter 44 is varied in accordance with the now varying relative linear speeds of the scanning beams as they sweep across the work piece 25. The end result is the same, namely, the counter 44 is driven at rates proportional to the linear speeds of the scanning beams as they sweep across the work piece surface.

The differential 5 is but one form of mechanism that is suited for the required change of angular speed, be itl eitherin the counter drive or in the scanning disc drive, to compensate for the varying relative linear speeds of the vseveral scanning beams as they sweep the work piece 25. In Fig. 14, for example, is shown another form. of mechanism that achieves substantially the same end result. Referring now more particularly to Fig. 14,

' a shaft |65 through a gear reduction box I5, as

in the Fig. 1 embodiment. On shaft |05 is mounted a one-turn clutch I4, as in Fig. 1, which drives a shaft I6I. On'the shaft IGI is secured a bevel gear |63, which meshes with a bevelled pinion |65 mounted on a countershaft |61 suitably supported in bearings |69 at right angles to the main shaft IBI. The countershaft |61 non-rotatably carries a wide pinion |1I. In the present embodiment, a scanning disc |13 is provided, which is non-rotatably mounted on a shaft |15 supported in suitable bearings |11. The center lines of shafts |61 and |15 intersect. Shaft |15 is provided with thrust bearings |16 and |18 and with a substantially constant brake I2.

The arrangement of the scanning holes in the disc' |13 is somewhat different from that in the Fig. 1 embodiment, and will be described in greater detail hereinafter. The illuminating and optical system of the present embodiment, however, is analogous to that of the Fig. 1 embodiment, and its elements are accordingly designated with the same reference characters. The same istrue of the electromagnetic clutch 35, multiplier gears 42, counter 44, coupling 45, hand wheel 46, brakes I2 and 41, periodic timing devices 31 and 38, photoelectric cell 29, amplifier 3|, relays 33 and 36, work piece 25, and reflector 21. In the present embodiment, the brakes I2 and 41 are mounted on the shafts |15 and 43, respectively, and the periodic timing devices 31 and 33 are mounted on the shaft |15. The multiplier gear 42 and counter 44 are calibrated as a unit and are reset to the correct starting position after the conclusion of an area measurement by means of the hand wheel as in the first embodiment. The oneturnclutch I4 is adjusted to start and stop the rotation of the shaft IBI when the disc |13 is in such a position that the dead region defined by the dead angle 6, to be described in greater detail hereinafter, is between the lenses 2| and 23 and preferably in such a position that the rst hole which is to begin the next scanning process is near the edge of the aperture 3|) of the mask 28. The periodic timing devices 31 and 38 are adjusted to perform their respective functions at the beginning and end of the scanning process as described hereinbefore inyconnection with the rst embodiment and therefore the external circuit of the relay 33 and the electromagnetic clutch 35 is broken throughout the dead portion ofthe cycle defined by the dead angle 0. The maximum angle through which the sleeve I I1 of the one-turn clutch I4 can rotate, relative to the shaft |6I, is a small angle relative to the dead angle 0 and the operation of the one-turn clutch I4 cannot produce an error in the measurement of area for reasons analogous to the reasons setforth hereinbefore in the description of the first embodiment.

Although the shafts I6I and |15 do not in general rotate at the same speed, the pitch diameters of the gears |63, |65, |1| and disc |19 are chosen so that said shafts require the same length of time to rotate through 360 degrees.

The other end of the scanning disc shaft |15 non-rotatably carries a disc |19, which is substantially identical in diameter to the disc |13. The disc |19 serves to mount an eccentric approximately circular row of upstanding pins |83, the projecting portions of which are given the contours of rack teeth, so that they suitably mesh with the teeth of the pinion |1I. The drive for the scanning disc |13 is thus as follows, from the drive shaft |05: Shaft |05 drives the one-turn clutch I4 which drives the shaft |6| which drives bevel gear |63, which drives bevel pinion |65, which drives pinion |1I, which drives disc |19 by engagement with teeth |83, which drives shaft |15, which drives the scanning disc |13. The assembly consisting of the discs |19 arid |13, shaft |15, periodic timing devices 31 and 3B and the drum of the brake I2 is statically balanced about the axis of the shaft |15.

The disposition of the scanning holes, now indicated generally by numeral |8I, on the scanning disc I13,is indicated in Figures 15, 16, and 17. The entire series of scanning holes I8I, it will be seen, seems to be arranged in a circle with its center slightly displaced from the center of the disc |13; as a matter of fact, this arrangement is not exactly circular, as will be pointed out hereinafter. All of the holes IBI are spaced at substantially uniform linear distances apart, around the approximate circle on the disc |13.

Hole IBIa, shown at the top of the disc in Fig. 15, is at the greatest distance from the center of the disc |13 of all of the holes I8I. Hole IBI, which is closer to the center of the disc |13 by a predetermined distance "h than the hole IBIa, is placed in the next position, on the series of holes, to the left of hole IBIB. This arrangement is shown in Fig. 16, but it is to be understood that in Fig. 16, for clarity, the distance "h has been exaggerated with respect to the angles shown, in order to make the arrangement more understandable. Hole ISIC, which is positioned hf units closer to the center of the disc |13 than is the hole Ilb, is located in the iirst angular position to the right of the hole IBIS. Hole IBId, which is "h units closer to the center of the disc |13 than hole IBIc, however, is located on the next angular position to the `left of hole Ilb. This left and right arrangement continues to the portion of the disc |13 diametrically opposite the portion occupied by hole IBIQ, which is shown, with exaggerations similar to Fig. 16, in Fig. 17. Hole I8Iz, which, of all the holes in the series, is

, closest to the center of the disc |13, is diametrical-A ly opposite hole IBIS.. Hole Iily, which is h units farther from the center of the disc |13 than is hole |312, is located on the next angular position to the right of hole |812. Hole I8IX, which is "h units farther from the center of disc |13 than is hole I8Iy, is located on the angular position to the left of hole I8 I z.

The other holes IBI on the disc |13 are arranged in similar manner, the entire series of holes thus resembling a circle, but, as will be seen from the foregoing description, this is not a true geometrical circle. It will be understood that the use of the letters of the alphabet as subscripts designating particular holes I8| is not intended to limit the number of holes IBI on the disc |13 to the number of letters in the alphabet. On the contrary, the number of holes ISI may be made any desired number, depending upon numerous factors, such as the number of scanning beams it is desired to produce for the particular kind of measurement in hand. In Fig. 15, for example, there is shown a total of eightyfour holes |8I, three of which I8|a, I8Ib and |8| are preferably covered to provide a dead angle 0 analogous to the dead angle of the Fig. 1 embodiment.

The dead angle 0 is provided to eliminate measurement error due to possible slight underrunning or over-running of the one-turn clutch I4 as discussed hereinbefore in the description of the Fig. 1 embodiment. The dead angle 0 is defined as the minimum angle through which the shaft |15 must be turned after the completion of the scanning by the last hole |8|e, for example, in order to bring the hole lld, for example, into position to begin scanning. In the description of the disc |13 hereinbefore presented the inclusion of the holes Isla, |8|b and |8| was for the sake of simplicity, but evidently it is unnecessary to produce said holes. It will be understood that the appearance of the holes |8|a. |8|b and |8| in Fig. 15 as well as the mention of sai'd holes in the description hereinbefore is intended to represent the positions which said holes would occupy, which positions must be known in order to design the disc |19.

The driving pins |83 on the disc |19 are disposed in a series the line of centers owhich is preferably identical, both in size and shape, to the line of centers of the series of holes |8| on the scanning disc |13. It is not necessary that there be one pin |83 for each hole |8|, but this is a desirable minimum number of pins.

In Fig. 18, for example, a total of one hundred and sixty-eight pins |83 are provided, or, in other words, two pins |33 for each hole |8|. It will be understood that pins |83 are provided in positions corresponding to those of the covered or non-provided holes |8|a, |8|b, and |8|c. The line of centers ofthe pins |33 is the same, both as to form and as to size, as the line of centers of the holes |8|. The outermost pin |835 is positioned on the drive disc |19 at such a position that when it is on the center of the pinion |1|, the hole position |8| is in the center of the optical system represented by the lenses 2| and 23. The same relation exists between the innermost pin |83z and the innermost hole I|z,'and all other corresponding intermediate holes orhoie positions and pins.

The width of the pinion 1| is such that, Without longitudinal motionhit is capable of engagiing al1 o`f the pins |83 drgthe disc |19, from the outermost pin |838 to the'iinn'ermost pin |83.

'I'he disposition of pins |83 and holes |8| as thus described results in the achievement of a drive for the scanning disc |13 that may be explained as follows, assuming the shaft |61 to be rotating at constant speed: Whatever hole |8| happens to be in potion between the lenses 2| and 23, is moving at an-angular rate determined lby the distance of its corresponding pin |83 from the center of the drive disc |19. 'I'his is true because the pinion |1| rotates `at a constant speed, but it drives the disc |19 at varying radii, thus changing the angular speed of rotation of the disc |19 and hence the angular speed of rotation of the scanning disc |13. Each hole |8| is driven across the optical system at the same linear speed as all of the other holes, although its angular speed is diierent from that of any of the other holes.

It is evident that the mechanism of the present embodiment is such that the linear speeds of all holes |8| are constant relative to the speed of shaft |6| regardless of the speed of said shaft,

and therefore that all of the holes |8| produce scanning beams which move across the work piece 25 with the same linear speed relative to the angular speed of the shaft |6|; henceI accuracy is achieved in the registering or recording of area by the counter 44 in the same general manner as was the case with the Fig. 1 embodiment.

It will now be seen why all of the holes ISI, and pins |83, are arranged in an approximately .of the Fig. 1 embodiment.

circular, eccentric line of centers, rather than in a spiral series. By the approximately circular arrangement speciiied, the change of angular spacing of the adjacent pins |83 is so small as to be without any substantial binding eiect on the engagement of the pinion |1| with the pins |83, around the entire line of pins |83. If a spiral arrangement of pins |83 were used, there would be a considerable radial gap between the first or outermost pin of the spiral and the last or innermost pin of the spiral, and 'this gap would represent a relatively great and abrupt change in the angular spacing of the pins |83, which abrupt change in spacing would interfere considerably with the meshing of the pins |83 with the pinion |1|.

In operation, the embodiment of Fig. 14 acts i'n a manner analogous to that hereinbefore described for the embodiment of Fig. 1. The motor i3 runs constantly, thus driving the shaft |05 constantly. When a work piece 25 is in the correct position in front of the reflector 21, the knob |41 is pulled and the one-turn clutch I4 permits the shaft |6| to make one revolution.

which causes the disc |13 to make one revolution. When the first hole |8| begins to scan the combination of reflector 21 and work piece 25, periodic timing device 31 closes the external circuit of the relay 33 and the electromagnetic clutch 35 through the action of the relay 36 and the photoelectric cell 29 is placed in control of the electromagnetic clutch 35 in such. a way that when the light of a scanning beam is not re'- fiected to the cell 29 by the reiiector 21, due to interception of the beam by the work piece 25, the electromagnetic clutch 35 is energized and an integrating operation is performed by the counter 44 in the same manner as in the Fig. l embodiment. g, When the last hole |8| completes its scanning of the combination of reflector 21 and work piece 25, periodic timing device 38 acts through relay 36 to open the external circuit of the relay 33 and the electromagnetic clutch 35 so that the counter cannot increase its reading until the beginning of the next scanning process. Following the completion of the scanning process, and at the completion of the one revolution of the shaft |6| permitted by the oneturn clutch I4, the shaft IBI stops rotating.

After the reading of the counter 44 has been noted and recorded, the'coupling 45, connecting the electromagnetic clutch 35 to the shaft 4|, is opened and the hand wheel 46 is rotated in the forward direction until the counter 44 reads exactly zero or any other predetermined number. The coupling 45 is then closed to connect the electromagnetic clutch 35 to the shaft 4| and` the apparatus is ready for another measurement of area.

Because of the disposition of the scanning holes |8| on the disc |13, the order in which the increments of the work piece 25, are scanned, is somewhat different from the order in the case It will readily be seen, however, that the order of scanning is without effect on the accuracy of the area measurement, since all of the increments are scanned once and only once, although adjacent increments are not in general scanned by successive beams.

Because of the unequal angular spacing of the holes |8I, the aperture 39 of mask 28 in the Fig. 14 embodiment will not have the same shape as in the Fig. 1 embodiment.

The diameter of any scanning hole |1 in the Fig. i embodiment, or itl in the Fig. 14 embodiment, should be such that the spot it produces on the work piece 25 is not greater inv diameter than the Width of the increment to be scanned thereby. In the drawings, the diameters of holes il and iti are necessarily enlarged, relative to the diameters of the respective scanning discs, for clarity.

The angular spacing ofthe scanning holes of either embodiment may readily be calculated from the width of the work piece 25 to be measured and the constants of the optical system employed.

Many of the devices shown in the drawings may readily be replaced by other devices performing the same functions in the system. For example, the reector 2l instead of being spherical may be made up of a plurality of relatively small, proper- 1y positioned plane mirrors. 'Ihe electromagnetic clutch 35 and counter M, constituting the integrating mechanism of the apparatus illustrated, may be replaced as below indicated, or may have any other form, such as an electrically operated ratchet motor. The one-turn clutch lil may be replaced by any other device which will perform the same function.

The photosensitive device 29 may be of any type of sumclent sensitivity for the purposes required.

As statedV hereinbefore the size and position of the reflector 2l are such that the conical projection of the scanned area on the plane of the Work piece 25 does not extend beyond the conical projection of the reflector 21 on the plane of the Work piece 25, said scanned area being limited by the aperture 30 of mask 28. If the action of the relay 33 is reversed so that the electromagnetlc clutch 35 is mechanically connected to the counter 4i when any scanning beam is reflected to the photosensitive device 29, the conical projection of the scanned area on the plane of the work piece 25 can be evaluated by operating the area measuring apparatus in the usual manner when no work piece 25 is in position to intercept scanning beam light. With the action of the relay 32 still reversed in said manner the area of a work piece 25 can be found, after operating the area measuring apparatus in the usual manner with the Work piece 25 in position for measurement, by subtracting the observed area from the known value of the conical projection' of the scanned area on the plane of the worl; piece 25. 'I'his involves no change in the principles of the invention as it merely means designating the uncovered conical projection of the scanned area on the plane of the work piece 25 as the area to be measured, and for convenience said method of determining the area of a work piece 25 may be called the subtraction method."

If the subtraction method of area measurement is used certain modifications in the design of the reflector 2l may be made advantageously. For example, if the reflector 21 is made of a discontinuous type, wherein reflecting areas alternate with areas not reflecting sumcient light to the photosensitive device 29 to actuate it, the light received by the photosensitive device will be pulsating, and the output of the amplifier 3| is an alternating current which may be rectified and used to operate an integrating mechanism controlled by direct current, or which may be used without rectification, if at a suitable frequency,` to actuate a self-starting synchronous clock-type motor as an integrating mechanism.

'I'he same effect may be achieved with a continuously relecting mirror 21 by making the lightsource I9 operate intermittently, or by placing a continuously operating shutter or light chopper in such a position as to interrupt the scanning beams.

It may here be pointed out that photosensitive devices are essentially detectors of radiation. Thus, the radiations usable in the present inventionA are not confined to visible light rays but may include supersonic waves, infra-red rays, and ultra-violet rays, providing these radiations are not harmful to the material being measured, and provided suitable radiation detectors are used. All such radiations are comprehended to be within the scope of the term light as herein used.

One of the principal objects of the present invention is to attain high accuracy in the measurement of area. It is readily understood that the accuracy of measurement of any quantity, such as area, is limited by the precision with which the various parts of the measuring apparatus function and is limited by the manner in which the measuring apparatus is used. It is also readily understood that perfect measurements of any quantity, such as area, are impossible to make, and that commonly the operator of the measuring apparatus realizes that thereis always present a minimum error in a measurement of the quantity, said error being caused by imperfections in the design or/and construction of the apparatus and by imperfect methods of use of the apparatus. As an example, in the measurement of length with the aid of a common steel rule or scale the accuracy of the measurement is limited by a number of factors such as imperfections in the lay-out of the lines on the scale,

the resolving power of the eye which may be determined, for example, by the quality of the eyesight or by the quality of the illumination, the neness and proximity of the rulings, and the care with which the scale is used.

Since many errors may enter into the measurement of any quantity it is necessary to reduce each error to such a magnitude that the maximum resultant error is not greater than the allowable error set by some predetermined accuracy which suiiices.

In commercial practice it is usual to deiine the error in terms of the maximum magnitude of the quantity which can be measured so that, for example, if th.;- maximum length L which a device can measure in a single complete measurement is l0 inches the maximum relative error may be expressed as 0.1 per cent. of 10 inches, so that any one observed length may diner from the true length by as much as 0.01 inch, regardless of whether the actual length is 0.1 inch or 10 inches, for example.

In the measurement of a quantity by a series of steps, such as the measurement of the individual areas of different parts of a surface and then adding together the results of the separate measurements, there are three types of errors which must be taken into consideration, viz., random errors, constant errors and periodic errors. Random errors, such as might result from backlash in a mechanical linkage or in a gear train, often have a tendency to cancel one another but in many cases they do not cancel one another cornpletely and therefore should be reduced as much as possible by precision construction. Constant errors may be due to incorrect proportionality between speeds of moving parts, for example, or

sol

failure of the counter to record the last unit in a series of units being integrated, for example. Constant errors are generally easily eliminated or rendered negligible through correct design. Periodic errors are those which periodically repeat themselves, usually in a predictable manner,

It is to be understood that in designing the.

herein described area measuring apparatus due attention has been paid to all potential sources oi error and that many of the features of the invention have been introduced for the purpose of reducing the cumulative error to such an extent thatv the measurement of area may be made with a degree of accuracy hitherto unattainable with commercial area measuring machines. Although great care has been exercised in the design of the hereinbefore described embodiments of the invention, it is assumed and expected that equally great care will be exercised in the construction and use of the area measuring apparatus. l

In the hereinbefore described embodiments of the invention, sources of measurement error lie in the optical system, including the lenses 2| and 23 and the disc I, and in the linear speeds of the scanning beams as they sweep 'across the work piece 25 relative to the angular speed of the shaft 43 of the counter 44. The lenses 2| and 23 are preferably of such high quality that the images of the holes |1 in the disc on the work piece 25 are sharply defined and the median lines of the paths Ra, Rb Re, etc. of said images on the work piece 25 are true arcs of circles having radii which are proportional to the radii of the respective holes I1. The holes |1 in the disc are precisely located both angularly and radially and the thickness of the disc around each hole |1 is made as small as practicable, as by grinding, for example.

The linear speeds of the scanning beams as they sweep across the work piece 25 relative to the angular speed of the shaft 43 of the counter 44 are determined by a number of factors in addition to those which have been discussed in detail hereinbefore. The relative linear speeds of the scanning beams are affected by all types of speed errors in the moving parts of the apparatus beyond the one-turn clutch i4 such as the gears 39, for example, and by vibration and accidental movement of the scanning apparatus, or of parts thereof, which may produce a movement of the light beam across the work piece 25 and so cause false measurement. The relative speed errors of moving parts rare eliminated as nearly completely as possible through precision construction of the component parts and any residual errors are reduced as required by any of the methods well known to and commonly used by instrument makers skilled in their art. For exampe, if the rate of rotation of the spur gear 53 is not proportional at all times to the rate of linear displacement of the rack 6| because of an error in the spacing or shaping of the teeth of either of said members, correction can be applied directly to the teeth of the gear 53 or the teeth of the rack 6|, or it can be applied indirectly to the contour of the cam so that the error in the relative rate of rotation of the gear 53 cannot produce a serious error in the relative rate of rotation of the disc Random speed rrors are eliminated as nearly completely as possible through precision construction and through rigidity of mounting of all parts such as the lenses 2| and 23, the mask 28 and the bearings of the shafts 3, 1, and. 61, for example. Backlash error of all moving parts such as the gears 39, for example, is reduced to a minimum through precision construction and through the introduction of the brakes |2 and 41 on the shafts 3 and 43, respectively, of the first embodiment and on the shafts |15 and 43, respectively, of the second embodiment. In the first embodiment, any backlash in the gears 41 and 59 of the differential 5, for example, may result in backlash between the shafts 3 and 1 during the time in which the disc loses its advanced angular displacement relative to the cam 65, but said backlash is easily reduced to such an extent that the brake I2 removes said backlash completely during the dead period of rotation of the shaft 1 defined by the dead angle Rotating parts, such as the cam 65 and the gear |19, are statistically balanced to prevent unwanted rotation due to the force of gravity.

It is important that the distance of work pieces 25 from the lens 23, measured along the axis of the lens 23, be constant and correct and that the plane of work pieces 25 be parallel to the plane of the disc because otherwise serious measurement errors may result. For the same reason it is important that the distance of the disc from the lens 23, measured along the axis of the lens 23, be constant and correct, and to insure this condition all lengthwise displacement cf the shafts 3 and |15 is prevented by suitable thrust bearings 8 and and |16 and |18, respectively.

None of the requirements hereinbefore men tioned for attaining high accuracy of area measurement is to be considered as a limitation of said accuracy, because the layout and construction of the apparatus is simple and straightforward and the required precision of design and construction of the apparatus falls within the limits of precision normally encountered in the design and construction of high grade chronometer mechanisms and high grade motion picture projectors,

,for example.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As many changes could be made in carrying out the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

We claimp.

1. In area measuring means, scanning means adapted to sweep scanning beams across a sur,- face to ce measured tracing concentric circular paths on said surface, and means rotating said scanning means in such manner that the linear speeds of all of said beams along said paths are substantially equal.

2. In area measuring scanning means adapted to sweep scanning beams across a surface to be measured tracing concentric circular paths on said surface, and means rotating said scanning means in such manner that the angular speed of said scanning means is progressively increased as the radius of said circular paths on said surface decreases.

aisance adapted to sweep scanning beams across a sur- .face to be measured tracing concentric circular paths on said surface, and means rotating said scanning means in such manner that the linear speeds of all of said beams along said paths are substantially equal, said last-named means including a shaft rotating at a predetermined angular speed, and a cam-controlled differential interposed between said shaft and said scanning means.

4. In area measuring means, scanning means adapted to sweep scanning beams across a surface to be measured tracing concentric circular paths on said surface, and means rotating said scanning means in such manner that the linear speeds of all of said beams along said paths are substantially equal. said last-named means including a shaft rotating at a predetermined angular speed, and a cam-controlled differential interposed between said shaft and said scanning means, the said cam being designed so that the diierential advances the scanning means relative to the said shaft in a predetermined manner during part of a single rotation, and then permits the scanning means to slow up until`joined by said shaft during the remainder of said single rotation.

5. In area measuring means, scanning means adapted to sweep scanning beams across a surface to be measured tracing concentric circular paths on said surface, and means rotating said scanning means in-such manner that the linear speeds of all of said beams along said paths are substantially equal, said last-named means including a shaft rotating at a predetermined angular speed, and a cam-controlled differential interposed between said shaft and said scanning means, the said cam having a spiral shape.

6. In area measuring means, scanning means adapted to sweep scanning beams across a surface to be measured tracing concentric circular paths on said surface, and means rotating said scanning means in such manner that the linear speeds of all of said beams along said paths are substantially equal, said last-named means comprising a crown gear of approximately circular shape, but rotating about an eccentric center, said crown gear -being connected for rotation with said scanning means, and a pinion engaging said crown gear and moving with substantially uniform angular speed.

'7. In area measuring means, a scanning disc having a series of scanning beam-forming holes therein, said holes being disposed at uniformlyv differing distances from the center of said disc, and means rotating the said disc in. such manner that the scanning beams produced by all of said holes move at substantially uniform linear speed relative to the vangular speed of the disc.

8.' In area measuring means, a scanning disc having a series of scanning beam-forming holes therein, said holes being disposed at uniformly diiering distances from the center of said disc, and means rotating the said .disc in such manner that the scanning beams produced by all of said holes move at substantially the same linear speed relative to the angular speed of the disc, the said holes being substantially all disposed at uniform linear distances apart near the periphery of said disc.

9. In area measuring means, a scanning disc having a series of scanning beam-forming holes therein, said holes being disposed at uniformly differing distances from the center of the disc,

4 i 1 a and means rotating the said disc in such manner that the scanning beams produced by al1 of said holes move at substantially the same linear speed relative to the angular speed of the disc, the said holes being disposed at predetermined angular distances apart, the line of centers of said holes being a spiral on said disc.

10. In area measuring means, a scanning disc having a series of scanning beam-forming holes therein, said holes being disposed at uniformly diiering distances from the center of said disc, and means rotating the said disc in such manner that the scanning beams produced by all of said holes move at substantially the same linear speed relative to the angular speed of the disc, the said holes being substantially all disposed at substantially uniform linear distances apart near the periphery of said disc, the line of centers of said holes on said disc being approximately a circle, the center of which is eccentric with respect to the center of the disc.

11. In area measuring means, a scanning disc having a series of scanning beam-forming holes therein, said holes being disposed at uniformly differing r distances from the center of said disc, and means rotating the said disc in such manner that the scanning beams produced by all'of said holes move at substantially the same linear speed relative to the angular speed of the disc, the said holes being disposed at substantially uniform angular distances apart, except for two holes,

which are spaced apart a greater angular distance said scanning disc, and a cam controlling the op.

eration of said differential.

13. In area measuring means, a scanning disc having a series of scanning beam-forming holes therein, saidholes being disposedatuniformly differing distances from the center of said disc, and means lrotating the said disc in such manner that the scanning beams produced by all of said holes move at substantially the same linear speed relative to the angular speed of the disc, the said lastnamed means comprising a second disc rotatable with said scanning disc, said second disc having pins mounted thereon along a line of centers equivalent in size and shape to the line of centers of the holes in said scanning disc, and a rotating pinion engaging said pins to drive the said second disc.

i4. A scanning disccontaining a spiral arrangement of beam-controlling holes, the distances of successive holes along the spiral, from the center of'the disc, increasing by a uniform distance, said holes being spaced apart by equal angular distances, except for two of theV holes, which are spaced apart an angular distance in' excess of the angular distancesbetween any two of the re- 

